1. Field of the Invention
The present invention relates to collecting and analyzing blood samples and, more particularly, to a method and apparatus for collecting blood samples for determining the amount of heavy metals such as lead contained therein.
2. Description of the Related Technology
The Center for Disease Control ("CDC") in Atlanta has published new guidelines for preventing and treating lead poisoning in children. CDC is dropping the "threshold of concern" blood level from 25 to 10 micrograms per deciliter for children younger than age six, and is recommending direct blood lead measurement over the currently used erythrocyte protoporphyrin assay for detecting these lower lead levels.
Medical research has found that exposure to lead and consequent lead poisoning is devastating in developing children, especially from birth to six years of age. The investigation has disclosed that the currently acceptable blood lead level cut-off of twenty-five micrograms per deciliter still causes a significant decrease in the intelligence quotient (IQ) of children. The proposed 10 microgram per deciliter acceptable standard makes current screening methods for lead poisoning ineffective because of the lack of sensitivity. Currently, free erythrocyte protoporphyrin (FEP) and zinc protoporphyrin (ZPP) are commonly used mass screening methods of detecting lead poisoning. At 10 micrograms per deciliter of blood lead, the FEP and ZPP methods are not effective diagnostic measurements.
Testing blood for lead content is not, however, limited to just children. Workers exposed to lead in the work place must also be screened for excessive levels of lead in their blood. Testing of blood for lead content is generally considered the most incontrovertible evidence of lead absorption. Thus, there is need for blood testing of both children and adults for excessive lead levels in their blood.
Some of the currently used methods of blood lead analysis are graphite furnace atomic absorption spectrometry (GFAA), anodic stripping voltammetry (ASV), atomic absorption spectrometry (AAS) with methylisobutylketone (MIBK) extraction, and filter paper Delves cup (FPDC) with AAS. These blood lead analysis methods, however, each have their drawbacks.
GFAA provides a sensitive and accurate procedure for testing for lead content in blood, however, the GFAA-method requires expensive instrumentation and supplies such as graphite tubes.
The ASV method uses less expensive instrumentation but is still relatively slow and the instrument stability is difficult to maintain, especially at low concentrations of lead in the blood. Relatively long analysis time and expensive sample preparation materials make the ASV procedure cumbersome and unacceptably costly for large volume laboratories. The MIBK method requires two to four milliliters of blood and such a large sample volume is not desirable in screening programs for children.
A preferred method for blood lead testing is the FPDC which requires a small volume of blood and minimum sample preparation. A typical analysis time of 15 seconds for a sample is readily obtainable. The FPDC method is simple and rapid in processing and yields a sensitive, reproducible and accurate result.
The FPDC method utilizes filter collection paper that is spotted with a blood sample taken from a finger prick or earlobe puncture. The blood sample taken is of capillary blood from the surface of the skin and is of minimal amount. Blood from a vein is not required and the capillary blood drawn from the shallow skin prick is easily applied to the filter collection paper by spotting with a capillary tube (heparinized) that is used to collect the blood sample from the subject. A petri dish may be used to contain the filter collection papers and also to reduce the paper exposure when the blood is not being spotted onto the paper.
Once the filter collection paper is spotted with the blood sample, the paper is allowed to dry. The filter collection paper containing the dried blood sample may be stored in a glassine open-end envelope for transportation to the testing laboratory.
To analyze the blood sample, it is first necessary to obtain a disk of filter collection paper of an area which, when spotted with blood, holds a known volume of blood. A procedure to do this is more fully described in an article by Carl Vereby et al., Rapid, Sensitive, Micro Blood Lead Analysis: A Mass Screening Technique for Lead Poisoning, 15 Journal of Analytical Toxicology 237 (1991). This article describes a procedure for punching out the paper containing a dried blood sample. A hole punch is used to punch out one-quarter inch diameter disks that define a standard area of collection paper containing the dried blood sample. These punched out dried blood samples are next placed in a Delves cup and introduced into a high temperature means such as a flame. The collection paper ignites and burns creating an ash. This ash of paper and dried blood are then atomized by heating in a crucible of an atomic absorption spectrometer ("AAS") in which the lead concentration in the blood may be determined.
The AAS method for determining concentrations in blood samples is highly accurate for detection of lead in the 5-200 microgram per deciliter range, however, the burning of the paper to ash results in smoke and soot that carbonizes the heating crucible used to atomize the sample for testing in the AAS system. The resulting soot requires that the AAS system crucible be cleaned frequently, thereby increasing testing costs and slowing the number of tests that are possible in a given time period. In addition, when the paper is burned in the crucible, the formation of smoke from the paper burning tends to mask those spectral peaks which indicate the presence of trace amounts of lead.
What is needed is a method and apparatus which does not produce undesirable by-products that tend to mask the lead trace in the heated vapor, yet allows a simple, efficient and cost-effective means for testing lead concentration in blood samples utilizing a lead detection system such as, for example, an AAS system. It is therefore an object of the present invention to obtain the desired components of a blood sample containing lead in a solution that may be placed directly into a lead determining system, such as an AAS furnace, for spectral measurement of the lead atoms which may then be used to determine the amount of the lead concentration in a given volume of blood.